title: Mutagenesis of the L, M, and N subunits of Complex I from Escherichia coli indicates a common role in function.
abstract: BACKGROUND
  The membrane arm of Complex I (NADH:ubiquinone oxidoreductase) contains three large, and closely related subunits, which are called L, M, and N in E. coli. These subunits are homologous to components of multi-subunit Na(+)/H(+) antiporters, and so are implicated in proton translocation.
  
  
  RESULTS
  Nineteen site-specific mutations were constructed at two corresponding positions in each of the three subunits. Two positions were selected in each subunit: L_K169, M_K173, N_K158 and L_Q236, M_H241, N_H224. Membrane vesicles were prepared from all of the resulting mutant strains, and were assayed for deamino-NADH oxidase activity, proton translocation, ferricyanide reductase activity, and sensitivity to capsaicin. Corresponding mutations in the three subunits were found to have very similar effects on all activities measured. In addition, the effect of adding exogenous decylubiquinone on these activities was tested. 50 µM decylubiquinone stimulated both deamino-NADH oxidase activity and proton translocation by wild type membrane vesicles, but was inhibitory towards the same activities by membrane vesicles bearing the lysine substitution at the L236/M241/N224 positions.
  
  
  CONCLUSIONS
  The results show a close correlation with reduced activity among the corresponding mutations, and provide evidence that the L, M, and N subunits have a common role in Complex I.
authors.affiliation: Department of Biological Sciences, Southern Methodist University, Dallas, Texas, United States of America.
authors.forename: Jose
authors.initials: J
authors.lastname: Michel
authors.forename: Jessica
authors.initials: J
authors.lastname: DeLeon-Rangel
authors.forename: Shaotong
authors.initials: S
authors.lastname: Zhu
authors.forename: Kalie
authors.initials: K
authors.lastname: Van Ree
authors.forename: Steven B
authors.initials: SB
authors.lastname: Vik
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D042967:Electron Transport Complex I / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism / Q000502:physiology*; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics* / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology; D015971:Gene Expression Regulation, Enzymologic / Q000502:physiology; D008239:Lysine / Q000235:genetics; D008954:Models, Biological; D008958:Models, Molecular; D008969:Molecular Sequence Data; D046912:Multiprotein Complexes / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D016297:Mutagenesis, Site-Directed; D030781:Organisms, Genetically Modified; D017433:Protein Structure, Secondary; D021122:Protein Subunits / Q000737:chemistry / Q000235:genetics / Q000378:metabolism / Q000502:physiology
chemical_list: D046912:Multiprotein Complexes; D021122:Protein Subunits; D042967:Electron Transport Complex I; D008239:Lysine